Spread band tuning device



Aug. 28, 1945. v. R. BECK 2 ,383,462

SPREAD BAND TUNING DEVICE Original Filed 00$. 10, 1940 2 Sheets-Sheet lAug. 28, 1945. v R BECK 2,383,462

SPREAD BAND TUNING DEVICE Original Filed Oct. 10, 1940 2 Sheets-Sheet 2|4T5|5|51 [5.3 15.5 1'5 17 17.7 an 17.5 us 5.5

PM; Aug. 28, 1945 SPREAD BAND TUNING DEVICE Virgil R. Beck, Elmhurst,11]., assignor to Zenith Radio Corporation, a corporation of IllinoisOriginal application October 10, 1940, Serial No.

360,870. Divided and this application September 19, 1942, Serial No.458,951

7 Claim.

This invention relates to spread band tuning circuits and isparticularly useful in radio receiving sets, but is applicable to anyapparatus employing tuning circuits, such as signal generators,transmitters, etc.

This application is a division of the copending application Serial No.360,670, filed October 10, 1940, for Spread band tuning device, andassigned to the same assignee as the present application.

It is well known that various portions of the radio spectrum are muchmore crowded than other portions. For example, in short wave broadcastreception it is found that frequencies, and corresponding portions ofthe dial, from 9.5 to 9.7 megacycles and from 11.7 to 11.9 megacycles,being respectively the 31 and 25 meter short wave bands, are verycrowded, whereas the frequency band from 9.7 to 11.7 megacycles containsvery few stations. Likewise, the frequency bands from 15.1 to 15.35 andfrom 17.75 to 17.85 megacycles, being respectively the 19 and 17 metershort wave bands, are crowded, while the band from 15.35 to 17.75megacycles contains practically no stations. In conventional receiverswherein modified straight line frequency tuning condensers areordinarily employed to tune through a relatively wide frequency band, itis found to be almost impossible to tune accurately a station in thecrowded portion of the dial, for the reason that a Very slight movementof the tuning control results in a considerable change in the capacityof the condenser, and accordingly, in the resonant frequency of thetuned circuit. Thus, a slight rotation of the dial is apt to tune thereceiver through the frequencies of a number of stations, resulting ingreat difilculty in accurately tuning a desired station and eliminatingothers.

The terms spectrum" and bands" are used throughout this specification intheir commonly accepted meanings-for eXampIe the radio frequencyspectrum includes all of the above mentioned allocated wave bands, 1.e.: the 31, 25, 19 and 17 meter bands and the so-called "dead ranges offrequency similar to the range from 9.7 to 11.7 megacycles and 15.35 to17.75 megacycles mentioned above. Furthermore, it is understood that theterm broadcast is used in the manner as defined in present daydictionaries and means any desired radiotelephonic and radio telegraphictransmission of intelligence. Also, the term "switchless is used todistinguish the present tuning system over the well-known prior artsystems employing band switching arrangements for switching tunedcircuits in the receiver for reception in two adjacent bands.

It is an object of this invention to provide a new and improved tuningcircuit which produces rapid frequency changes in certain frequencyranges and slow frequency changes. in other ranges, upon movement of thetuner at a uniform rate throughout its range of adjustment.

' It is another object of the invention to provide such a tuning circuitwhich spreads the scale indications of those portions of the radiospectrum containing large numbers of stations and which condenses thescale indications of those portions which are little used.

A further object of the invention is to provide such a tuning circuit inwhich the capacitive reactance is so modified locally as to producedesired rapid frequency changes in certain ranges and' desired slowchanges in other ranges.

In accordance with the invention the tuning circuit is arranged andconstructed so that a single scale encompasses at least two separatecrowded portions of the frequency spectrum, and so that these twoseparate crowded portions are expanded substantially uniformly, theintermediate portion of the frequency spectrum being condensed on thescale.

The features of my invention which Ibelieve to be novel are set forthwith particularity in the appended claims. My invention itself, both asto its organization and manner of operation, together with furtherobjects and advantages thereof, may best be understood by reference tothe following description taken in connection with 5 the accompanyingdrawings in which:

Figure 1 is a perspective view of a condenser constructed in accordancewith the present invention;

Figure 2 illustrates the shape of a single rotor plate of the condenserof Figure 1;

Figure 3 is a perspective view of two condensers mounted on a singleshaft, one being constructed in accordance with my present invention;

Figure 4 is a perspective view of a modified form of condenser similarto that illustrated in Figure 1;

Figure 5 illustrates a single stator plate of the condenser of Figure 4;

Figure 6 is a view, partly in section of a varied according to myinvention, as illustrated in Figures 1 and 4;

Figure 9 is a schematic diagram of tuned amplifier circuit including avariable inductance such as illustrated in Figures 6 and 7;

Figure illustrates a pair of tuning scales arranged to cooperatewith apointer adjustable simultaneously with the condenser of Figure 8 or theinductance of Figure 9;

Figure ll is a schematic diagram of a modified form of tuning circuitarranged to produce results as the circuits of Figures 8 and 9; and

Figures 12 and 13 are other modified forms of the circuit of Figure 11.

With reference to Figure 1, the condenser is provided with rotor platesl0 mounted on a shaft H, the rotor plates being adapted to be rotatedinto position between stator plates H which are secured together bysuitable fastening means (3.

The effect of this type of rotor plate can best be described withreference to Figure 2. As the rotor plate is rotated from the positionshown in Figure 1 into the space between the stator plates, it isapparent that segment A first enters this space. As the radius and thearea of segment A are relatively large, a substantial change is producedin the capacity of the condenser for each increment of rotation. As thesegment B begins to enter the space between the stator plates, theamount of change of capacity for a given rotary movement is reducedmaterially since segment B is of small radius and area, and eachincrement of rotation introduces only a small additional area. Assegment C enters the space between the rotor plates, the capacity'of thecondenser again changes very rapidly for the same rate of rotationbecause of the large radius of the segment being introduced. Segment Dproduces a slow change of capacity at the same rate of rotation for thesame reason as segment B. Segment E again produces a rapid change incapacity similar to that of segment A.

This invention is particularly adapted for use in short wave broadcastreception, since it is in the short wave broadcast band that localovercrowding of stations occurs. In a radio receiver designed to receivestandard broadcasts, as well as short wave broadcasts, a secondcondenser, such as a modified straight line frequency condenser may beprovided, which cooperates with more or less uniform markings on thestandard broadcast scale. These two condensers may be separatelyprovided. However, it has been found advantageous to combine the twocondensers into a single unitary structure.

Such a combined unitary structure is illustrated in Figure 3, in whichthe modified rotor plates l 0 and the standard rotor plates are mountedupon the same shaft II, and are all electrically connected. The statorplates 12 may be divided into two sections between which electricalinsulation H is provided. That is, two separate condensers may be builttogether, one serving for the standard broadcast range, and the otherfor the shortwave range. The rotor plates are usually connected toground and, therefore, there is no necessity for electrically insulatingthe two sections of rotor plates of the condenser, although thesesections may be insulated if required by the circuit employed. Theelectrically insulated stator sections of the condenser are connected toa suitable band changing switch (not shown) so that either one may beincluded in the tuned circuit, depending upon the station which it isdesired to receive. As

shown in Figure 3, the rotor plates exceed by one the number of statorplates, so that when the rotor plates are in engagement with the statorplates they surround the stator plates. Substantial space is providedbetween the two stator sections of the condenser, so that the capacitybetween the two stator sections is minimized.

In Figure 4 a modification of my invention is illustrated in which therotor plates III are sol d and in which the stator plates I! have beenperforated to produce the desired effect. The contour of a stator plateis clearly illustrated in Figure 5, wherein segments A1, Bl, C1, Di andE1 correspond to segments A, B, C, D and E in Figure 2. It is apparentthat the working of this modification is the same as that of Figure 1,the direct being produced by the stator plates as distinguished from therotor plates.

Figure 6 illustrates a variable inductance of the variable permeabilitytype which may be used to produce an effect similar to that of thevariable condensers of Figures 1 and 4. This variable inductance mayinclude an insulating tube 3| about which a coil 32 is wound. Theconductors forming the coil are uniformly distributed over the tube 3 I.A core 33 of low loss magnetic material is arranged to move into and outof the tube 3|.

The configuration of the core is such as to produce the desired result,such as that produced by the condensers of Figures 1 and 4. The largesection A: at the end of the core 33 produces a rapid change ininductance when inserted in the tube 3| and accordingly 9. large changeof frequency. As section B: enters the tube 3|, the rate of change offrequency is lower, since the cross-sectional area of the core issmaller. Section C2, which is of large cross-section, produces a rapidchange of frequency. Section Dz, like section 3:, produces a slow changeof frequency because of its small cross-section. Section E: of largecross-section, like section C2, produces a rapid change of frequency. Itis apparent that by suitably adjusting the cross-sectional areas of thesections referred to, this variable inductance of Figure 6 may be .madeto produce the same effect as the previously described variablecondensers of Figures 1 and 4.

Figure 7 illustrates a variable inductance having a uniform core 36arranged to move into and out of a non-uniformly wound inductance coil.The inductance illustrated is designed to produce'a result similar tothe result produced by the re actances illustrated in Figures 1, 4 and6. It includes a tube 35 about which a conductor may be wound insections. each section having the requisite number of turns to producethe desired rate of change of frequency for that section. Sections A3,C3 and E: are closely wound and contain many turns per unit length.Sections Ba and Do contain a few turns per unit length. It is evidentthat as a uniform core 36 enters the tube 35, there is produced insequence a rapid change, a slow change, a rapid change, a slow change,and a rapid change of inductance, and therefore of frequency.

While the condensers of the present invention as illustrated in Figures1 and 4, have been described as being constructed with either the statorplates or the rotor plates modified to expand certain portions of thespectrum while compressing other portions, it is apparent that the sameresult can be produced by partially modifying both the stator plates andthe rotor plates, so that the modified portions of both plates cooperateto produce the desired result. Similarly the inductances illustrated inFigures '7 and 8 achieve the desired result in the one case by reason ofa modified core shape and in the other case by reaaseaus son of modifiedwinding distribution. It is apparent that the desired results accordingto the invention may be produced by making both core shape and windingdistribution non-uniform so as to produce the'same result described asproduced by the non-uniformity of either one of these constructionalfeatures of the inductance.

In Figure 8. the condenser 9 is connected in shunt to an inductance il',illustrated as a transformer, and is acondenser such as that illustratedin Figure 1 or 4. The condenser 9 and inductance I 8' form a tuned inputcircuit for a stage of tuned amplification, in which the tuned frequencymay be adjusted according to my in-' vention.

In Figure 9 there is shown a similar tuned amplifier in which the tunedinput circuit includes an inductance 40, such as the inductancesillustrated in Figures 6 and 7. This inductance 40 is connected inseries with an inductance ll which is illustrated as an inputtransformer, and a fixed condenser 42 is connected in shunt to theseries combination of inductances l and II.

In Figure 10 there is illustrated a pair of scales suitable forcooperation with a pointer attached to the movable element of theinductance of Figure 9, or the condenser 9 of Figure 8. The upper of thetwo scales of Figure 10 shows that the portion of the frequency rangefrom 9.5 to 9.7 megacycles has been spread out considerably to take careof the large number of stations in that area. Likewise, from 11.7 to11.9 megacycles there are many stations. and this portion of the scalehas also been spread out considerably. The portion from 9.7 to 11.7,which contains few stations, has been crowded together. This upper scaleof Figure 10 shows that the two standard short wave bands from 9.5 to9.7 megacycles, and

from 11.7 to 11.9 megacycles have been spread substantially uniformlyand equally. Each of these two short wave bands covers 200 kilocycles,and each is spread for substantially the same linear distance along thescale. The segments B and D of the adjustable reactance in the tuningcircuit are so formed as to produce this substantially uniform spread ineach of the two separated spread band portions.

Comparing the shape of the condenser rotor plate illustrated in Figure 2with the lower scale of Figure 10, it is evident that segment A producesa rapid change in frequency from 18.5 to 17.85 megacycles. This insurescomplete coverage of the upper end of the range. When segment B isrotated into the space between the stator plates, the slow change ofcapacity and of frequency corresponds to the large distance on the scalebetween 17.85 and 17.75 megacycles. Then, as segment C enters betweenthe stator plates, the rapid change in capacity produces a large changein frequency corresponding to the relatively short distance along thelower scale from 17.75 to 15.35 megacycles. As segment D enters betweenthe stator plates, its slow change of capacity corresponds to the longpart of the scale between 15.35 and 15.1 megacycles. Segment E producesa rapid change of capacity from 15.1 to 14.5 megacycles so as to insurecomplete coverage of the lower end of the range.

In the previous paragraph the condenser has been described as coveringthe range from 14.5 to 18.5 megacycles. Thi condenser is also used tocover the range from 9 to 12.5 megacycles, by changing the inductancewith which it is connected in shunt so as to make the tuned circuitresonant within the range 9.0 to 12.5 megacycles.

- cycles.

That is, two inductances are used, one being connected in shunt with thecondenser for the high frequency range and the other for the lowfrequency range. The circuit is switched from one inductance to theother depending uponwhich wave band it is desired to tune.

Complete coverage of the range from'9 to 18.5 megacycles can also beaccomplished by a single condenser without a change of inductance byforming a condenser plate so as to give rapid coverage of the ranges 9.0to 9.5, 9.7 to 11.7, 11.9 to 15.1, 15.35 to 17.75, and 17.85 to 18.5megacycles; and to give slow coverage of the ranges between 9.5 and 9.7,11.7 and 11.9, 15.1 and 15.85. and 17.75 and 17.85 megacycles. That isto say. condensers in accordance with the present invention can beemployed wherever it is desired to extend substantially uniformlyselected portions of a tuning range while compressing intermediateportions of the range,

In the previously described circuits the desired results have beenproduced by forming one or more elements of the adjustable tuningreactance so as to give the desired non-uniform frequency change. InFigures 11, 12 and 13, similar results are produced by introducing into,or removing from, the tuning circuit one or more reactances separatefrom the variable tuning reactance. This is brought about by switchmeans operated in unison with the tuning reactance and arranged tocontrol the connection of additional inductance or capacity to thecircuit such as to vary the rate of tuning in the various sections ofthe radio frequency spectrum in the desired mannerwhile maintaining acontinuous change of frequency across the entire range.

In Figure 11 there is illustrated a tuning circuit having a variablecapacity II and a fixed inductance l2. Operatively connected to thevariable condenser H are switches 18 and H. The switch 13 is adapted tointroduce additional capacity into the circuit while switch 14 isarranged to introduce additional inductance to the circuit. When thecondenser H is adjusted to minimum capacity to tune the circuit to highfrequencies in the desired range, switch 14 connects inductance 15 inseries with inductance 72 across condenser II, the only capacity incircuit. Since condenser H is the only capacity in the tuning circuit. achange in its capacity produces a relatively rapid change of frequency.

At a desired point in the adjustment of condenser H, as its capacity isincreasing, switch 14 removes inductance 75 from the circuit andintroduces another inductance 16, which is a smaller inductance.Simultaneously, switch 13 introduces condenser into the circuit insh'unt to the condenser H. The condenser 89 and the inductance 16 areselected to be of such appropriate values that there is no change in theproduct of inductance and capacity, and therefore no change infrequency, as the switches 18 and H move from one contact to the next.Thus, the frequency immediately before the change is the same as thefrequency immediately following the change.

With the additional capacity 80 in the circuit in shunt to capacity 1|,further adjustment of condenser 'II to increase its capacity results ina slower change of frequency because of the reduced rate of change ofthe overall to capacity. This effect is used to spread out a desiredportion of the spectrum, as from 17.85 to 17.75 mega- At the endof thatportion of the spectrum, as condenser II is being adjusted in thedirection of still greater capacity, switches 18 and move to the nextcontact, thereby introducing inductance 1"; into the circuit andremoving condenser 88 therefrom. The inductance 11 is of suitable valueto maintain the product of inductance and capacity constant, andtherefore to keep the frequency the same as it was immediately beforecondenser 88 was removed from the circuit. The inductance 11 is largerthan the inductance it, as is necessary because the condenser 98 hasbeen removed from the circuit. With inductance 11 in the circuit, andcondenser 98 out of the circuit, the change of frequency is rapid, sincea change in the capacity of condenser 1i now produces an equal change inthe overall capacity of the tuning circuit. The part of the frequencyspectrum covered by the tuning circult with inductance 11 in the circuitand condenser 88 out may, for example, be used to cover a little usedportion of the spectrum rapidly, as from 17.75 to 15.35 megacycles.

When condenser ii is increased in capacity until the tuning circuit istuned to the lowest frequency in this little used range of the spectrum,switch 14 disconnects inductance 11 from the circuit and introducesinductance 18, and simultaneously switch 13 reconnects condenser 88 inthe circuit. The inductance 18 is of the value necessary so that theseswitching operations produce no change in frequency of the tuningcircuit. The inductance 18 is smaller than the inductance 11 tocompensate for the introduction of condense 88 in the circuit.Adjustment of the condenser 1| with these connections results in a slowchange of frequency for the same reason as when the inductance 18 andcondenser 88 were in circuit. The ortion of the frequency spectrumcovered by adjustment of the condenser 11 under these conditions maycorrespond, for example, to that portion between 15.35 and 15.1megacycles.

At the end of that portion of the frequency spectrum, switch 14 removesinductance 18 from circuit and introduces inductance 19 into thecircuit, while switch 18 removes condenser 88 from the circuit. Thisswitching operation is also carried out without any change of frequencybecause. the inductance 19 is made of proper value. Further increase ofcapacity of condenser 1| produces a rapid change in frequency.

It is evident from the above description that the circuit of Figure 11produces in sequence a rapid change, a slow change, a rapid change, aslow change, and a rapid change of frequency, with uniform change incapacity of the variable condenser 1|. It is evident that the shape ofthe plates of condenser 1| may be modified to produce the substantiallyuniform frequency change over the two short wave bands on each of thescales illustrated in Figure 10. If desired, separate fixed condensersfor each of the five tuning ranges, corresponding to each of theinductances to 19 may be employed instead of a single condenser 88.

In Figure 12 is illustrated a circuit which produces an effect similarto that of the circuit of Figure 11. This circuit includes a variablecondenser 85, a fixed inductance 88, and a fixed inductance 89.Connected to operate in unison with the condenser 85 are switches 81 and88. At the high frequency end of the scale, inductances 8B and 89 andthe variable condenser 85 are inserted. Adjustment of condenser 88 undersuch condition produces a relatively rapid change of frequency. At adesired frequency switch 81 in- After condenser 88 is inserted andinductance- 89 is removed, the rate of change of frequency with changein capacity of the variable condenser 88 is materially reduced. At theend of the desired spread band portion, switch 81 removes condenser 98from the circuit and substitutes condenser 9|, a smaller condenser.Simultaneously switch 88 removes the short circuit from the inductance89, so that it is again effective in the circuit. Condenser 9| is ofsuitable value so that the switching operation is effected without achange of frequency to which the circuit is tuned. After this switchingoperation the rate of change of frequency with change of capacity of theadjustable condenser 88 is rapid.

As the capacity of condenser 85 is further increased, switch 81 removescondenser 91 from the circuit and substitutes condenser 92, a largercondenser, in place thereof. Switch 88 again removes inductance 89 fromthe circuit by short circuiting it. Condenser 92 is of suitable value tomaintain the frequency the same before and after the switchingoperation. After this switching operation the rate of change offrequency is again slow over a desired range, after which switch 81removes condenser 92 from the circuit and introduces condenser 98, asmaller condenser than 92. Simultaneously, switch 88 removes the shortcircuit from inductance 89 so that it is again effective in the circuit-Condenser 93 is of suitable value to maintain the frequency the samebefore and after the switching operation. Thereupon further increase ofcapacity of the condenser 85 produces a rapid change of frequency. It isthus evident that this circuit also produces in sequence a rapid change,a slow change, a rapid change, a slow change, and a rapid change offrequency.

In Figure 13 there is illustrated a circuit arranged to produce the sameeffect and including a variable inductance such as those illustrated inFigures 6 and 7. This circuit includes a fixed condenser 95 and avariable inductance 98. Operatively connected to the inductance 98 formovement in unison therewith are switches 91 and 98. At the highfrequency end of the portion of the spectrum covered by the tuningcircuit, inductance 98 and condensers 95 and I88 are inserted. Withthese connections a small change in inductance produces a large changein frequency. At a desired frequency, switch 98 removes condenser I88from the circuit and at the same time switch 91 places the additionalinductance 99 in circuit in series with inductance 98. Inductance 99 andcondenser I88 are of suitable values so that the frequency with whichthe tuning circuit is resonant is the same before and after theswitching operation.

With the added inductance 99 in circuit, change of frequency upon changein the inductance 98 is slow so as to. spread the frequencies of adesired portion of the spectrum. At the end of that band over whichfrequencies are so spread, switch 91 again removes inductance 99 fromthe circuit by short circuiting and switch 98 places a relatively largecondenser MI in circuit, the condenser l8l having a value such that afrequency Inductance 89 and condenser change is not produced by theswitching operation.

Further adjustment of inductance 96 produces a rapid change in frequencywith such switching connections. As the inductance further increases,.switch 9|! removes condenser IOI from circuit and substitutes therefora smaller condenser l02, while switch 9'! simultaneously reinsertsinductance 89 in the circuit. Condenser I02 is of suitable value tomaintain the frequency the same before and after the switchingoperation. This change in the circuit spreads another portion of theband, so that further increase of the inductance 96 produces arelatively slow change of frequency.

Upon still further increase in inductance 96, switch 91 removes theinductance 98 from circuit by short circulting it, and switch 98 removescondenser I02 from circuit and substitutes a larger condenser I03 in itsplace. Again, there is no change of frequency before and after theswitching operation. After this circuit change, change of inductance 96produces a rapid change of frequency. It is evident that this circuitproduces much the same effect as the circuits of Figures 11 and 12.

The circuits of Figures 11 through 13 are particularly suited forproducing the results illustrated on the two scales of Figure 10. Aspointed out .previously, the spread-out portions of each of these scalesare spread substantially uniformly and equally, the intermediateportions on each scale being compressed. It is evident that thesecircuits may be employed without band switching to produce over onescale all of the changes in tuning rate illustrated in Figure on twoscales by merely providing the requisite number of elements to cover theentire range.

In the drawings only those elements of tuning circuits necessary toproduce an operative circuit have been disclosed. It is evident thatadditional refinements in turning circuits may be employed inconjunction with the present invention without departing from the spiritthereof. The switches employed in the various circuits of Figures 11, 12and 13 may be mounted upon the same shaft or other movable member usedto tune the variable tuning member, and may be of the snap-action type.However, these switches may be separate from the tuning member and maybe operated therefrom by any suitable means such as gears, belt chaindrives, etc.

While I have shown and described particular embodiments of my invention,it will be obvious to those skilled in the art that changes andmodiilcations may be made without departing from my invention in itsbroader aspects, and I, therefore aim in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of my invention.

I claim:

1. In a radio receiver for receiving signals at any frequency within alarge portion of the radio frequency spectrum having a plurality ofseparated allocated bands in each of which there are a relatively largenumber of broadcast signals differing in frequency by relatively smallamounts, each pair of adjacent allocated bands being separawd by arelatively large contiguous so-called "dead" range of frequencies withinwhich range there are a relatively few broadcast signals differing infrequency by relatively large amounts, the combination of a switchlesstuning circuit having a fixed inductance'and a variable capacitance,said capacitance having two relatively movable members, one of which isa movable tuning element continuously adjustable for varying thecapacitance of said circuit to tune said circuit continuously withinsaid portion of the spectrum to any desired frequency within said bandsand so-called "dead" range, and a control element for continuouslymoving said tuning ele ment through a first series of positions andthrough intermediate positions to and through a second series ofpositions, within which first and second series of positions saidcircuit is tuned to desired frequencies within two of said separatedallocated bands, said intermediate positions corresponding to resonantfrequencies within the intervening so-called "dead" range, at least oneof said relatively movable members being shaped to vary relativelyrapidly the resonant frequency of said circuit within said interveningso-called dead range for a given rate of displacement of said tuningelement through said intermediate positions and being shaped to vary theresonant frequency of said circuit within one of said two separatedbands at a substantially lower rate for the same rate of displacement ofsaid tunins element through said first series of positions and atsubstantially the same rate within the other of said two separated bandsthrough said second series of positions.

2. In a radio receiver for receiving signals at any frequency within alarge portion of the radio frequency spectrum having a plurality ofseparated allocated bands in each of which there are a relatively largenumber of broadcast signals differing in frequency by relatively smallamounts, each pair of adjacent allocated bands being separated by arelatively large contiguous so-called dead range of frequencies withinwhich range there are a relatively few broadcast signals differing infrequency by relatively large amounts, the combination of a switchlesstuning circuit having a fixed inductance and a variable capacitance,said capacitance having two relatively movable members, one of which isa rotatably movable tuning element continuously adjustable for varyingthe capacitance of said circuit to tune said circuit continuously withinsaid portion of the spectrum to any desired frequency within said bandsand so-called "dead range, and a control element for continuously androtatively moving said tuning element through a first series ofpositions and through intermediate positions to and through asecondseries of positions, within which first and second series ofpositions said circuit is tuned to desired frequencies within two ofsaid separated allocated bands, said intermediate positionscorresponding to resonant frequencies within the intervening so-calleddead" range, at least one of said relatively movable members beingshaped to vary relatively rapidly the resonant frequency of said circuitwithin said intervening so-called dead range for-a given rate ofdisplacement of said tuning element through said intermediate positionsand bein shaped to vary the resonant frequency of said circuit withinone of said two separated bands at a substantially lower rate for thesame rate of displacement of said tuning element through said firstseries of positions and at substantially the same rate within the otherof said two separated bands through said second series of positions.

3. In a radio receiver for receiving signals at any frequency within alarge portion of the radio frequency spectrum having a plurality ofseparated allocated bands in each of which there are a relatively largenumber of broadcast signalsdiffering in frequency by relatively smallamounts, each pair of adjacent allocated bands being sepa rated by arelatively large contiguous so-called dead" range of frequencies withinwhich range there are a relatively few broadcast signals differing infrequency by relatively large amounts, the combination of a switchlesstuning circuit having a fixed inductance and a variable capacitance,said capacitance having two relatively movable members, one of which isa movable tuning element continuously adjustable for varying thecapacitance of said circuit to tune said circuit continuously withinsaid portion of the spectrum to any desired frequency within said bandsand so-called dead" range, movement of said movable tuning elementproducing substantially no change in the magnitude of said inductivereactance, said movement of said movable tuning element changing theresonant frequency of the tuned circuit solely by producing capacitancechanges in said variable capacitance, and a confrequency of said circuitwithin said intervening so-called dead range for a given rate ofdisplacement of said tuning element through said intermediate positionsand being shaped to vary the resonant frequency of said circuit withinone of said two separated bands at a substantially lower rate for thesame rate of displacement of said tuning element through said firstseries of positions and at substantially the same rate within the otherof said two separated bands through said second series of positions.

4. In a radio receiver for receiving signals at any frequency within alarge portion of the radio frequency spectrum having a plurality ofseparated allocated bands in each of which there are a relatively largenumber of broadcast signals differing in frequency by relatively smallamounts, each pair of adjacent allocated bands being separated by arelatively large contiguous so-called dead range of frequencies withinwhich range there are a relatively few broadcast signals differing infrequency by relatively large amounts, the combination of a switchlesstuning circuit having a fixed inductance and a variable capacitance,said capacitance having two relatively movable members, one of which isa movable tuning element continuously adjustable for varying thecapacitance of said circuit to tune said circuit continuousl within saidportion of the spectrum to any desired frequency within said bands andso-called dead" range, and a control element for continuously movingsaid tuning element through a first series of positions and throughintermediate positions to and through a second series of positions,within which first and second positions said circuit is tuned to desiredfrequencies within two of said separated allocated bands, saidintermediate positions corresponding to resonant frequencies within theintervening so-called dead range, at least one of said relativelymovable members having two portions of relatively small area separatedby a portion of relatively large area, said member being shaped to varyrelatively rapidly the resonant frequency of said circuit within saidintervening so-called "dead range for a given rate of displacement ofsaid tuning element through said intermediate positions and being shapedto vary the resonant frequency of said circuit within one of said twoseparated bands at a substantially lower rate for the same rate ofdisplacement of said tuning element through said first series ofpositions and at substantially the same rate within the other of saidtwo separated bands through said second series of positions, saidportions of relatively small area corresponding to said separated bands.

5. In a radio receiver for receiving signals at any frequenc within alarge portion of the radio frequency spectrum having a plurality ofseparated allocated bands in each of which there are a relatively largenumber of broadcast signals differing in frequency by relatively smallamounts, each pair of adjacent allocated bands being separated by arelatively large contiguous so-called dead" range of frequencies withinwhich range there are a relatively few broadcast signals differing infrequency by relatively large amounts, the combination of a switchlesstuning circuit having a fixed inductance and a variable capacitance,said capacitance having two relatively movable members, one of which isa movable tuning element continuously adjustable for varying thecapacitance of said circuit to tune said circuit continuously withinsaid portion of the spectrum to any desired frequency within said bandsand so-called dead range, and a control element for continuously movingsaid tuning element through a first series of positions and throughintermediate positions to and through a second series of positions,within which first and second series of positions said circuit is tunedto desired frequencies within two of said separated allocated bands,said intermediate positions corresponding to resonant frequencies withinthe intervening so-called "dead" range, at least one of said relativelymovable members having a pair of cutout portions, said member beingshaped to vary relatively rapidly the resonant frequency of said circuitwithin said intervening so-called dead" range for a given rate ofdisplacement of said tuning element through said intermediate positionsand being shaped to vary the resonant frequency of said circuit withinone of said two separated bands at a substantially lower rate for thesame rate of displacement of said tuning element through said firstseries of positions and at substantially the same rate within the otherof said two separated bands through said second series of positions,said output portions corresponding to said two separated bands.

6. In a radio receiver for receiving signals at any frequency within alarge portion of the radio frequency spectrum having a plurality ofseparated allocated bands in each of which there are a relatively largenumber of broadcast signals differing in frequency by relatively smallamounts, each pair of adjacent allocated bands being separated by arelatively large contiguous so-called dead" range of frequencies withinwhich range there are a relatively few broadcast signals diflering infrequency by relatively large amounts, the combination of a switchlesstuning circuit having fixed inductance and a variable capacitance, saidcapacitance having at least one fixed plate and at least one platespaced therefrom and parallel thereto and rotatalbly mounted forrelative movement with respect to the fixed plate, the overlap areabeing dependent upon the location of said movable plate relative to saidfixed plate, the amount of said capacitance depending upon the amount ofsaid overlap area, the position of said rotataibly mounted platerelative to said fixed plate being continuously adjustable for varyingthe capacitance of said circuit to tune said circuit continuously withinsaid portion of the spectrum to any desired frequency within said bandsand so-called "dead range without substantial change in the qualityfactor of the circuit, and a control element for continuously androtatively moving said rotatably mounted plate through a first series ofpositions relative to said fixed plate and through intermediatepositions to and through a second series of positions, within whichfirst and second series of positions said circuit is tuned to desiredfrequencies within two of said separated allocated bands, saidintermediate positions corresponding to resonant frequencies within theintervening so-called "den-d range, said fixed and movabl plates beingso shaped that the derivative of their overlap area-location functionhas a relatively large magnitude through said intermediate positions andrelatively small magnitudes through said first and second series ofpositions.

7. In a radio receiver for receiving signals at any frequency within alarge portion of the radio frequency spectrum having a plurality ofseparated allocated bands in each of which there are a relatively largenumber of broadcast signals differing in frequency by relatively smallamounts, each pair of adjacent allocated bands being separated by arelatively large contiguous so-called "dead" range of frequencies withinwhich range there are a relatively few broadcast signals diflering infrequency by relatively large amounts, the combination of a switchlesstuning circuit having at least two units presenting impedance to theflow of current, one of said two units having primarily inductance andthe other having primarily capacitance, at least one of said two unitshaving two relatively movalble members, one of which is a movable tuningelement continuously adjustable for varying the inductance-capacitanceproduct of said circuit to tune said circuit continuously within saidportion of the spectrum to any desired frequency within said bands andsocalled dead range without substantial change in the quality factor ofthe circuit, and a control element ailixed to said tuning element forcontinuously moving said tuning element through a first series ofpositions and through intermediate positions to and through asecond'series of positions, within which first and second series ofpositions said circuit is tuned to desired frequencies within two ofsaid separated allocated bands, said intermediate positionscorresponding to resonant frequencies within the intervening socalled"dead" range, at least one of said relatively movable members beingshaped to vary relatively rapidly the resonant frequency of said circuitwithin said intervening so-called "dead" range'lor a given rate ofdisplacement of said tuning 'element through said intermediate positionsand being shaped to vary the resonant frequency of said circuit withinsaid two separated bands at substantially lower rates for the same rateof displacement of said tuning element.

VIRGIL R. BECK.

